Differential drive for flour mill roll stands and the like



April 17, 1951 Y K. MCCLELLAND 2,549,501

DIFFERENTIAL DRIVE FOR FLOUR MI L ROLL STANDS AND THE LIKE Filed July 21, 1949 Patented Apr. 17, 1951 UNITED STATE S PATENT OFFICE DIFFERENTIAL DRIVE FOR FLOUR MILL ROLL STANDS AND THE LIKE Kenneth McClelland, Chica n), Ill., assignor to John E. Mahoney, Chicago, Ill.

Application July 21, 1949, Serial No. 106,037 h 4 Claims.

roll to which power is applied. The slow roll of each pair tends to travel at the same peripheral speed as the fast roll due to the torque transmitted by the grain being fed between the rolls. In order to insure that the slow roll'turns at the desired slOWer s eed, this roll of each set is connected by means of pulleys and belting to a main drive shaft. In most roll stands the main drive shaft is connected to a tunnel shaft which, in conjunction with belt connections between said tunnel shaft and the slow rolls, serves to provide the desired speed differential between the fast and slow rolls. The problem of providing a suitable diiferential drive connection between the slow rolls and the tunnel shaft has proved to be very troublesome and requires excessive maintenance. Since the main drive for the fast rolls is a flat belt which runs over a pulley on the tunnel shaft, some means for adjusting the tension of the .main belt must be provided. Such means consists of a screw adjustment for raising and lowering the tunnel shaft and its associated main belt drive pulley. It is customary in a roll stand for each slow roll to have a separate belt connection with the tunnel shaft. It therefore becomes apparent that adjustment of the tunnel t..

shaft to provide suitable tension for the 'main drive belt cannot be made without disturbing the adjustment for either or both of the slow roll belts or tilting the tunnel shaft so that it is no longer parallel with the rolls. It has been standard practice to run the slow rolls with tilted tunnel shafts in order to maintain proper belt tension. This procedure is however, very undesirable because the beltstend to ride to one side of the pulleys which causes excessive wear on the belt edges.

pulleys on the tunnel shaft requires very tight belts and make it necessary to employ much wider pulleys and belts than are required to carry the load, in order to prevent slipping. In addi tion, increased belt tension has induced bearing failure.

The milling process, employing many roll stands, is a gradual reduction performed by feed- 2 ing to each roll stand one classification of the material being processed, reducing it by a defi: nite grind, then classifying the product of that roll stand for appropriate 'regrinding by one or more other roll stands. The rate of production of a mill as a whole is determined by the'maintea nance of the grind assigned to each rolljstand. Any variation in the grind of any roll stand will necessitate change in the distribution of the prod- 9 uct of that stand and upset the balance of work for subsequent roll stands, some being overloaded and, some underloaded, with consequent impairment of the efficiency of the mill. thing which most commonly causes variation in the grind of a roll stand and consequent upsetting of the balance of work for subsequent roll stands is change in the speed differential between ,the fast and the slow rolls arising from slipping of a differential belt. Correct tension of the short differential belts is highly important.

- It must be sufficient to prevent slip under all normal conditions of operation of aroll stand, yet not so great as to produce such an amount of bearing friction as to induce bearing failure or such heating of a roll stand as to cause the production of inferior flour or to require excessive power for operation of the rolls. The correct difspeed variations of the slow rolls with a tachom- The short distance between the pulleys on the slow rolls and their related eter under various different belt tensions while the stand is grinding. The said tension should be sufficiently great, as aforesaid, to prevent slip.

and avoid excessive bearing friction under normal conditions of operation of a roll stand, but not so great as to prevent a belt from slipping off its pulleys in the event of a serious overloading.

of the rolls as, for example, when the rolls become choked by the material being ground.

The problem of correct belt tension and ad justability is rendered more critical than might be supposed because not only must re'adjustments be made after a new belt has worked out its first stretch but changes in humidity affect the length of belting so that the belts must be constantly,

The"

sufficient to introduce an undesirable variation in the product being milled in the roll stand.

V-belts have also been tried for the differential drive but these have not proved entirely eaisfactory because in the event that the ground hour is not carried away fast enough, the rolls will become choked. This means that it is desirable to throw off the differential drive quickly, thus permitting the rolls to run at about the same speed. Obviously, this cannot be done with a V- belt drive. As a result, millers have retained the old flat belt drive with its known disadvantages because proposed substitutes have proven to be even less satisfactory.

A primary object of the present invention therefore, is to provide an automatic tension control for the differential drive on roll stands which enables a flat belt to be employed on the differential drive end of the mill and at the same time permits the tunnel shaft to be maintained parallel with the rolls at all times.

A further object of th invention is to provide in a roll stand a single differential fiat belt drive and an automatic tension-mg means for the belt, the belt having sufficient slack to permit normal adjustments of the tunnel shaft to secure proper tension on the belt driving the fast rolls.

Further objects will be apparent from the specification and drawings in which:

Fig. l is a perspective of a detail of a flour mill roll stand showing the main drive and the differential drive for the rolls; and

Fig. 2 is a schematic end view of the differential drive of l on a reduced scale.

A preferred form of roll stand of the type used in flour mills is driven through the main drive shaft 5, main pulley 5, and main driving belt Belt 5 passes upwardly and around pulleys ii and S on the fast rolls [9 and H which are in turn journaled at i2, i2 on frame rails 13, $3 of the roll stand. Belt 1 passes downwardly between pulleys 8 and 9 and under a pulley M on tunnel shaft is which is journaled in bearings 15 and if adjustably mounted in brackets 58 and iii The slow rolls 2i} and 2 l are journaled in bearings 22, 22 likewise supported on rails i3, i3. The

- slow roll shafts 21a and 2i?) eat-end in an opposite direction from the driving end of the stand and are provided with pulleys 23 and 2: 3. A single flat belt 25 passes over pulleys 23 and 24 and under pulley 26 on the opposite end of tunnel shaft i5. It will be understood that the ratio of pulleys 23, 2d, 25 and I4 is such that rolls 2?} and 2| turn at a predetermined and substantial peripheral speed slower than rolls l and H. In effect, the friction between the fast and slow rolls of each set that is present when grainis being fed into the machine, tends to equalize the peripheral speeds of the fast and slow rolls so that the difierential drive through pulleys 23, 24, 26, tunnel shaft i and pulley i4 is in effect a braking torque rather than a driving torque.

According to the present invention separate means of any suitable type may be provided in conformance with prior common practice for independently effecting vertical adjustments of the respective end portions of the tunnel shaft Hi. The present invention makes possible, however, the use of a single means common to both end portions of the tunnel shaft 15 for vertically adjusting both end portions of said shaft simultaneously. One such means is illustrated in the drawings as comprising a horizontal shaft 23 extending transversely of the roll stand shown and having thereon bevel gears 32, 3.2 in mesh with bevel gears 3i, 3! on vertical screws 29 and 30 which are threaded in the tunnel shaft bearings it and H, respectively. On the shaft 28 is a hand wheel 2! for effecting its rotation and thereby simultaneously adjusting the bearings 15 and H, vertically in their brackets I8 and I9, respectively, due to the driving connections between said shaft 28 and the screws 2Q and 30.

As explained previously, it is highly desirable witha flat belt drive to maintain the tunnel shaft E55 as nearly parallel to rolls H], H and 2 2i as possible to prevent belts l and from riding on one edge of the pulleys. The present invention permits such parallel adjustment to be made in accordance with the desired tension on belt '7 by means of a loaded pivotal idler pulley 33 which is pivoted at 34 and loaded by means of weight 35 operating on arm 35 through cable 3'! passing over pulley 38 (Fig, 2). Suiiicient slack is provided in belt 25 to permit the related end of the tunnel shaft i5 to partake of its full range of vertical adjustment. While the idler pulley adjustment has been shown in conjunction with the differential drive between the slow rolls and the tunnel shaft, it will be understood that an idler pulley may be used on the fast roll drive at the opposite end of the roll stand or at both ends, which would permit the use of a fixed tunnel shaft.

As previously stated, it is hightly desirable to maintain correct tension in the differential belt 25. The correct tension can be deterr. ined by varying the weight 35 while operating the roll stand under normal load and observing with a tachometer the slip (increase in speed) of the slow roll pulleys. The correct tension is that which is just enough to prevent slip. When the required weight has been ascertained, it remains fixed and, therefore, maintains the correct belt tension. The weight finally used may be either the variable experimental weight or any desired equivalent weight. Alternatively a suitable spring may be used in lieu of a weight. In any event, the correct tension will permit the belt readily to slip off its pulleys in the event of serious overloading of the roll stand and thus will avoid damage to the rolls as well as possible fire which sometimes occur as a result of excessive differential belt tension.

The chief advantage of my construction therefore, resides in the fact that the tunnel shaft may be adjusted to provide the correct tension in the drive belt and that the correct tension is automatically supplied to the other belt. In other words, the tunnel shaft may be maintained parallel to the axis of the rolls at all times. The main drive belt may be installed new when the tunnel shaft is at the top of its adjustment and the main belt willnot have to be shortened until the tunnel shaft has been adjusted to its maximum displacement. This feature avoids incorrect adjustment in either belt and substantially reduces bearing failures which may be due to excessive differential belt tension. Also, damage to the differential belt due to improper alignment,

which in turn causes the belt to run off one side of the pulleys, is eliminated.

A further advantage of the present construction resides in the fact that narrower pulleys may be employed than heretofore since the center distance on conventional mill stands has been relatively short, and excessively wide belts and pulleys have been found necessary. The present construction, by increasing the contact are of the belt 25 on pulleys 2 and 2%, enables balancing of the respective loads on said belt and thus enables such narrower belt and pulleys to be employed without loss of power. This advantage is of "importance since space is at a considerable premium in many flour mills. The elimination of two coaxial pulleys (one for each slow roll) on shaft [5, further enables a reduction in the overall length of the roll stand.

Having thus described my invention, I claim:

1. In a grind mill roll stand having two pairs of rolls each comprising a fast roll and a slow roll, a pulley fixed to each fast roll at one side of the stand, a pulley fixed to each slow roll at the other side of the stand, a tunnel shaft disposed substantially parallel to said fast and slow rolls and adjustable toward and away from the latter, a pair of pulleys on said tunnel shaft one in the plane of the pulleys fixed to said fast rolls and the other in the plane of the pulleys fixed to said slow rolls, a drive shaft having a pulley thereon, a drive belt extending from said drive shaft pulley over said fast roll pulleys and the related pulley onsaid tunnel shaft, a difierential belt connecting said slow roll pulleys with the related pulley on said tunnel shaft, and means automatically maintaining said differential belt under a constant predetermined tension suflicient to prevent slip of the same relative to its related pulleys under normal load conditions of the roll stand, but insufficient to prevent said belt from readily slipping off its pulleys in the event of abnormal loading of the roll stand, regardless of adjustments of said tunnel shaft toward or away from said rolls and regardless of variations in length of said differential belt.

2. In a grind mill roll stand having two pairs of rolls each comprising a fast roll and a slow roll, a pulley fixed to each fast roll at one side of the stand, a pulley fixed to each slow roll at the other side of the stand, a tunnel shaft disposedsubstantially parallel to said fast and slow end portions of thetunnel shaft simultaneously. 7

rolls and adjustable toward and away from the latter, a pair of pulleys on said tunnel shaft one in the plane of the pulleys fixed to said fast rolls and the other in the plane of the pulleys fixed to said slow rolls, a drive shaft having a pulley thereon, a drive belt extending from said drive shaft pulley over said fast roll pulleys and the related pulley on said tunnel shaft, a differential belt connecting saidslow roll pulleys with the related pulley on said tunnel shaft, an idler wheel engaging said differential belt, and means automatically maintaining said idler wheel urged against said differential belt under a constant predetermined pressure effective to produce in said belt sufficient tension to prevent slip of the same relative to its related pulleys under normal load conditions of the roll stand but insufficient to prevent said belt from readily slipping 01f its pulleys in the event of abnormal overloading of the roll stand, regardless of adjustments of said tunnel shaft toward or away from said rolls and regardless of variations in length of said differential belt.

3. A grind mill as set forth in claim 1 including a single means effective to vertically adjust both end portions of the tunnel shaft simultaneously.

4. A grind mill as set forth in claim 2 including a single means effectiveto vertically adjust both KENNETH MCCLELLAND.

REFERENCES CITED The following references are of record in the file of this patenti UNITED STATES PATENTS Number Name Date 178,063 King May 30, 1876 385,420 Mawhood July 3, 1888 463,414 Brown Nov. 17, 1891 832,361 Blevins Oct. 2, 1906 

